1. FIELD OF THE INVENTION
This invention relates to electronic control systems, and more particularly to devices of the type which convert mechanical movements into electrical signals.
2. DESCRIPTION OF THE RELATED ART INCLUDING INFORMATION DISCLOSED UNDER 37 CFR .sctn..sctn.1.97-1.99
U.S. Pat. No. 4,434,412 issued Feb. 28, 1984, and entitled "Contactless, Electric Control-Handle" relates to a controller of the type commonly known as a "joystick", which is employed either in the field known as "robotics", or with computer terminals for governing the movement of a cursor on a video display screen. The device employs a handle and a core pivoted on a base. An energizing coil is provided and is fed with alternating current, which in turn produces a fluctuating electromagnetic field around the core.
Four pick-up coils are also provided, spaced about the periphery of the energizing coil. Movement of the core toward any one of the pick-up coils increases the magnetic coupling between the energizing coil and the respective pick-up coil, causing an increase in the voltage induced in that coil. By providing four pick-up coils spaced circumferentially 90.degree. from one another, movement of the handle can be converted to two pairs of differential a.c. signals whose amplitudes can be correlated to the position of the handle in both the X-axis and Y-axis directions.
While the disclosed arrangement has utility for certain applications, it has been found that the cost is often prohibitive; in particular, in addition to the energizing coil, four individual pick-up coils are required; these are frequently bulky, consisting of many turns of very small gauge wire. The large number of turns is required in order to produce voltages of sufficient magnitude to be easily measureable. In addition, mounting of the four coils is difficult. If there existed any significant lack of symmetry between them, compensation was required so that a predetermined, precise "null" voltage could be obtained, corresponding to a neutral position of the handle and core. Such compensation was usually accomplished by adjusting the position of small core pieces associated with each of the pick-up coils.
With fine wire, connection to the coils was difficult because there was a tendency for the wire to break, particularly at the coil itself. Reattachment was often inconvenient or impossible.
Another disadvantage of the patented device was that it was subject to error due to temperature drift, aging, and external magnetic fields in the environment with which the device was used.
Efforts to eliminate both the energizing and the pick-up coils have been made, but have not met with any degree of success so far as I am aware.
In particular, the use of a permanent bar magnet as a core has been tried, with the energizing coil omitted. In addition, four Hall-effect transistors have been substituted in place of the four pick-up coils, respectively. This arrangement provided two pairs of d.c. outputs which varied according to the position of the handle.
However, this construction suffered serious drawbacks. There occurred drift due to aging of the permanent bar magnet and changes in temperature. A particularly troublesome problem also arose in the presence of external magnetic fields, even that of the earth. Since the Hall-effect sensors responded to any type of magnetic fields, the existence of stray fields caused erroneous readings. Even the presence of a piece of iron that was only moderately magnetized, defeated the operation of such controllers.